View Full Version : SBC1 tune up advise

08-24-2008, 12:17 PM
I got this kinda POS 68' Camaro sport coupe with the ilustrious 275 hp 327 mill... Im trying to tune this thing up and make it run half way decent.

The owner is getting the correct CI manifold and quadra jet for it that ill have to install but my main question invloves setting timing.

This thing runs kinda ok, breaks up a little but doesnt seem to want to wind out at all... I manualy advance the distributor and that made it run about 50% better all over but has the hard crank issue when starting lol.

What kinda timing should this thing be seeing at idle and say 3000 rpms and do i just disconn the vacuum advance and get a timing light and crank it up to xx degrees and lock it down?

Im not used to work on this old ass stuff :rolf

08-24-2008, 12:35 PM
IIRC its 8 OR 10 degrees with the advance disconnected and plugged at Idle. I used to run my 73 455 at 12 but it ran rich as shit.

08-24-2008, 12:38 PM
IIRC its 8 OR 10 degrees with the advance disconnected and plugged at Idle. I used to run my 73 455 at 12 but it ran rich as shit.

Yeah this thing is rich as shit at idle, and if i lean out the carb idle screws it it wont have it, it idles best about 800 rpms and fine tuning the mix screws but shes got way to much advnace for start up now.

08-24-2008, 12:45 PM
33-36 degrees of total timing.

Prince Valiant
08-24-2008, 01:17 PM
Using anywhere from 12-16 degrees initial is a good starting point generally for the older engines. The 327 will likely have a few degrees more timing tolerance/need built into vs that of a typical 350. Changing the timing shouldn't affect whether it's running rich or lean.

For a quadrajet, make sure you're pulling decent manifold vacuum if you think it's running too rich....sometimes if the guy's got a bigger cam and insist on a lowered idle speed, the power enrichment might cut-in (due to the low vacuum that'd result) a little, thus richening up the mixture. Of course, make sure that there are no vacuum leaks as that'll really throw you for a loop too...there can be internal vacuum leaks on the carb from things like worn throttle shafts and/or improper carb gaskets.

Set the timing for 12 degrees to start with the vacuum advance unplugged, and then tune for a lean best idle...get the idle speed to as low as it can go while idling steady...

From there, you can play with timing, advancing it and trying it, seeing where it runs.

Then from there, you'll have to just see where it advances at 3000rpm. If it's either much below 34 degrees, or much above 40 degrees, then you'll probably want to get the distributer recurved...in which case I'd shoot for 36-38 degrees total advance, all in by 2800 rpm.

You can, of course tune either by ear (highest idle) or by vacuum gauge (highest reading...but the reading increases due to idle speed increases so it's the same result as tuning by ear imo) however, this will generally leave you with too much advance, leaving you with hard starting, possibly with a after-fire at shut-down, and possible running problems at certain rpm's or with too much advance at cruise.

But best timing is, of course, going to be different for different combos, based on compression, valve timing, fuel used, rod length, stroke length, combustion chamber shape, etc. People generally have success with as low as 8 to as high as 17* initial based on various combos. It'll be experimentation to get the best result for this individual's car. Factory settings/service manuals usually call for timing on the low side compared to where the car will run it's best.

08-24-2008, 01:38 PM
put a ls1 in it.

08-24-2008, 03:59 PM
Thanks for the info Chris. Ive got some fresh plugs and wires, the old wires i can hear snapping from while its lidling lol Not to mention they are routed all through the engine compartment hahah.

08-24-2008, 05:23 PM
Well i got new plugs and wires in it, runs a shit ton better.

So i gotta timing light and set the base for 12 with the vaccum advance disconn and hose plugged, i rev it up to about 3k and its seeing about 25 degrees at best. So it looks like its gonna need a re-curve. Is this something i can kinda stab at my self? and how do i do it? flyweight springs?

Prince Valiant
08-24-2008, 09:54 PM
First try reving higher...see how far it goes before it stops advancing. 25 total doesn't seem right at all...as in it'd run kind of crappy i'd imagine. Some might go as high as 4600 rpm w/ stock springs (as it likely has) before it reaches full advance (sometimes I forget that not everyone has brand new-recurved distributers, lol)

Don't forget...springs only control the rate of advance. There is a slot that a weighted plate slides along that controls total advance...the springs can hold the plate in at low speeds, but centripetal force eventually overcomes the springs as engine rpm's increase, thus causing it to advance as the plates slide outward. Most factory distributers will actually have too much total advance built in when you get a good initial timing set (this is because they have overly low initial timing set for starting and emission purposes...yes, even before 1968 there were emission concessions), and one uses a bushing in the slots to limit total advance.

If that's the case, then lighter springs for quicker advance are in order...so that ideally you hit full advance b/w 2600-3000rpm or so for a mild-ish engine. You'll probably then have to adjust the vacuum advance to keep it at ~ 44-46* at whatever rpm you see at hwy speeds with the vacuum attached.

If you spin the thing up and you never see above 25*, then one of two things:

1. The hub on the harmonic balancer has shifted, giving you a false reading...this would also make it hard to find a good initial timing too though.

2. Or it's reasonably accurate and adjusting the total advance mechanism is in order...the easiest way is to simply take it to a shop and have them recurve it on a special machine for that purpose. You can do it on the car...it's can be tricky and where novices get into trouble.

Crane would sell the kit so you can play around adjusting total and advance rate. Another option would be simply to give summit a call...you can get a performance distributer for less ~80 bucks, with new shaft bushing for stable timing, a performance curve already programed in, etc.

In all honesty, it's probably going to fall in a decent total advance range, and at most you'll want to get the recurve springs from crane to get the timing in by 2600rpm, and then just readjust the total vacuum advance so it doesn't exceed 46* at around 2800-3000rpm w/ vacuum advance connected. Do that and you're bud will be amazed at the seat-of-pants difference in how the thing runs.

08-25-2008, 10:22 AM
well i gotta pull the dist anyway to put an intake on it, so ill dissassemble and clean that weight area which may be sticking too for all i know. Every adjustment i made so far has made a night and day diff.

The thing actually has torque and throttle responce now, it can wheel hop pretty good in 1st lololool

Ill **** with it some more when i fix some more stuff.

Prince Valiant
08-25-2008, 09:39 PM
Any of the local speed shops should have springs...hell, you can jury-rig a bushing if you should see too much advance.

Sprayaway Fox
08-27-2008, 03:37 AM
You will get 3 springs and new weights. Sounds like you will be either on the lighter spring or the medium one. Dont mix your stock weights with sprink kit. FOR ME i usually toss all my timing 32-36 in at 3100 if car is out at 6000. Then set idle. If it starts good cold or hot and doesnt ping when you get on it. I reccomend starting with the stock timing and go from their for a base. But I am not that great with that stuff, but my chevs ran nice, with that theory.

09-05-2008, 09:48 PM
SBC timing seems to be a "black art" to many folks, but it's really very simple to maximize the performance and fuel economy of a mild engine with just a bit of work. ANYONE can do this with a little care and the right tools. Figure on 2 hours to do this, and try to work undisturbed if possible. NOTE that a good dyno tune for $300+ will determine perfect timing, but this will get you 90% of the way there. This process assumes that you have an engine that is basically running with no significant issues.

Parts/Tools Needed
Willingness to get in and DO!
China marker or other means of marking the balancer.
Distributor advance kit. Any kit by a major manufacturer (Crane, Accel, Mr. Gasket, etc.) will work fine. The kit should be correct for your type of distributor (HEI or points) and include weights, springs and an advance limit bushing. I prefer this kit for 67-72: Mr. Gasket 927G for points-type, 929G for HEI. http://store.summitracing.com/partde...G&autoview=sku
Adjustable vacuum advance. As above, any good one will work. I prefer this kit for the 67-72: Crane 99601-1 for points, 99600-1 for HEI http://store.summitracing.com/partde...1&autoview=sku
Method for measuring advance. There are two basic ways to do this:
Advance timing light. This type of timing light has a method to set advance at the LIGHT so that the balancer mark is always on the '0' pointer. This is by far the best approach if you can afford it. This is an example light; buy the best one you can afford if you work on many cars. Equus 3555 or similar. http://store.summitracing.com/partde...5&autoview=sku
Timing tape. This is a tape that sticks the balancer and provides an advance reference. Clean the balancer with brake cleaner before applying. This kit has tapes for all different size balancers - MSD 8985 or similar http://store.summitracing.com/partde...5&autoview=sku

Verify TDC. DO NOT SKIP THIS STEP - your success in this process is all based on accurate TDC reference.
Buy or borrow a piston stop. These are cheap and likely available at your local parts store. Proform 66792 or similar http://store.summitracing.com/partde...5&autoview=sku
Buy or borrow an easy way to rotate the engine. Generally, doing this with the balancer bolt is a bad idea -especially since we'll need to rotate the engine both directions. Here's a tool that turns the flywheel. NAPA 2270 or similar http://store.summitracing.com/partde...5&autoview=sku
Pull the coil wire or if HEI, pull the B+ power wire.
Pull the #1 spark plug (first on the RIGHT when FACING the engine)
Put your finger over the spark plug hole, be SURE you are clear of anything that rotates, then have your friend (or remote starter switch) "bump" the engine with the starter until you feel the hole "burp" - this is the engine coming up on the compression stroke. If you don't have a remote starter switch, this may be the time to buy one - they're cheap and make this far easier.
Screw the stop into #1 spark plug and turn the inside screw on the stop either until it stops or until flush with the outside plug.
Rotate the engine one way with the flywheel tool - DO NOT use the starter - until the engine stops. Don't force it - it will come to a firm stop.
Make a mark on the balancer directly opposite the '0' marking on the timing tab.
Rotate the engine the other way until it stops and make another mark on the balancer directly opposite the '0' marking on the timing tab.
TDC compression is EXACTLY 1/2 BETWEEN THESE TWO MARKS. Use a steel rule or tape measure to measure between these two marks and make a permement mark 1/2 between. If the mark is very close to the stock slot in the balancer, call it good enough. Accuracy with this method is about +/- 2 degrees - which ain't bad
Turn the engine so that the TDC mark is opposite 10 or 12 degrees BTDC on the timing tab.
Remove the piston stop and re-install the #1 spark plug.
That wasn't hard, was it?
Mark the location of the #1 spark plug tower on the distributor body.
Remove the distributor cap.
Disconnect the vacuum advance.
Remove the distributor. DON'T try to do the rest of this process in the car...trust me
Chuck the distributor carefully in your vise.
Remove the rotor.
Remove the stock springs and weights and set them aside. If there is a limit bushing on the pin underneath the plate that the weights are on, remove it.
Install the limit bushing included in the advance kit. I generally give it a little squeeze with pliers to ensure a tight fit.
Install the weights included in the advance kit. Ensure they're clean of goo and move VERY easily. A little moly lube here is good.
Install the LIGHTEST springs in the advance kit. NOTE that every kit has different colors for their springs.
Install the adjustable vacuum advance and adjust as specified in the included instructions. Note that you may need to put a tube on the old advance unit to apply a vacuum (Mytyvac or your lungs ) to rotate the vacuum advance plate to get to the screws. You can manually rotate the plate as well.
Reinstall the rotor.
Reinstall the distributor. Note that the rotor will turn a little more than 2" as the drive gear engages the cam, so you'll want to start with the rotor about 2" behind the #1 mark you made on the distributor body. The distributor will be installed with the rotor pointing directly at the mark you made for the #1 tower with the vacuum advance pointing near the #4 cylinder (2nd on the LEFT side FACING the engine). If the distributor won't drop all the way in, the oil pump shaft is not aligned with the drive in the distributor - just carefully "bump" the engine until it drops.
Reinstall the cap.
Reinstall the coil wire or the HEI B+ power wire.
DO NOT reconnect the vacuum advance but ensure it is plugged.
The engine should start and run
Using your timing light or timing tape, ensure timing is fully advanced before 3000 RPM and adjust timing to 32-36 degrees at 3000 RPM.
Reset the idle to ~850 RPM and note the timing - this is your new initial timing;anything over 16 degrees requires additional debugging (PM me )
Driving test and adjustment
Expect that with no vacuum advance, you may have poor part-throttle driveability. Ignore this for the purpose of this test.
Make a few full-throttle runs. If you hear any pinging, replace the advance springs from the kit with the next heavier springs. This can easily be done with the distributor in the car, but don't drop 'em If you find you're "in between" two springs, it's OK to use two different springs to get it just right.
Reconnect the vacuum advance and make some part-throttle runs. If you hear any pinging at part throttle, adjust the vacuum advance to provide less advance (the unit will come with instructions). In rare cases, a vacuum advance limiter may be required; the Crane kit above comes with this limiter if needed and instructions how to install.

That's it! Seems like a lot of work when every step is outlined, but you'll find this to be a very straightforward process that can be completed in a few hours...and you'll have improved driveability, throttle response an fuel economy.

09-05-2008, 09:56 PM
stolen from another forum save at one time not sure when or where i got it from but very detailed.

09-06-2008, 09:12 AM
Got any pics of this kinda POS 68' Camaro? :)